Dynamic correlations in lipid bilayer membranes over finite time intervals.

This article focuses on developing and validating a theoretical framework to interpret experimentally measurable dynamic correlations between lipids in biological membranes, accounting for finite temporal resolution in single-molecule fluorescence measurements. Building on hydrodynamic models of membrane diffusion—particularly the Saffman–Delbrück (SD) theory and its extensions to two-leaflet membranes—the authors derive explicit expressions [Eqs. (24)–(28)] that relate measured lipid displacement correlations to the underlying two-body diffusion matrix, incorporating effects of finite illumination times that average out instantaneous correlations. These theoretical predictions are rigorously validated against Brownian dynamics simulations across various membrane models, including freely floating, supported, and black lipid membranes, demonstrating excellent agreement except at very small particle separations. The study further addresses experimental ambiguities in characterizing membrane parameters such as inter-leaflet friction and membrane viscosity, suggesting that combined measurements of lipid and transmembrane protein diffusion could resolve parameter degeneracies that lipid-only data cannot, thereby enabling a more complete hydrodynamic characterization of membranes.